Nickel powder production method and nickel powder production device

ABSTRACT

Provided is a method with which it is possible to prevent equipment, such as piping and valves, used to discharge and recover a nickel powder-containing slurry from a high pressure reaction tank from being damaged and trapping the nickel powder therein and to enable continuous operation, thereby improving the productivity. This nickel powder production method comprises a step of reacting a nickel sulfate-amine complex solution with hydrogen gas under high pressure in a reaction tank, thereby obtaining a nickel powder slurry containing nickel powder. The method is characterized in that the nickel powder slurry is discharged and transferred through discharge piping from the reaction tank in which the nickel powder-containing slurry has been produced, and then a washing solution is supplied to the discharge piping at a predetermined pressure to wash the discharge piping.

TECHNICAL FIELD

The present invention relates to a method of subjecting a nickelsulfate-amine complex solution to hydrogen reduction to obtain nickelpowder, and more specifically, to a nickel powder production method anda nickel powder production device which are capable of stablydischarging a nickel powder slurry produced in a reaction tank.

BACKGROUND ART

As a method for industrially producing nickel powder, there is a nickelpowder production method in which a raw material containing nickel isdissolved in a sulfuric acid solution, a treatment of removingimpurities contained in the raw material is performed, ammonia is thenadded to the obtained nickel sulfate solution to form nickel in the formof amine complex, and nickel in the nickel sulfate-amine complexsolution is reduced by bringing the nickel sulfate-amine complexsolution into contact with hydrogen gas, for example, at a hightemperature and a high pressure around 150° C. to 250° C. and 2.5 MPa to3.5 MPa to produce nickel powder (for example, Patent Document 1).

Such a method is a method by which a high quality nickel metal can beefficiently obtained with a compact facility; on the other hand, thereis a problem in that continuous operation which is industriallyadvantageous is difficult to perform since reaction is performed using ahigh-pressure container.

That is, the raw material and hydrogen gas are relatively easilysupplied to a high-temperature high-pressure reaction tank; on the otherhand, when a discharge side is constantly opened to external air, aninternal pressure of the reaction tank easily becomes equal to theexternal air, and reaction cannot be performed under a high pressure.For this reason, it is necessary to appropriately adjust the pressureinside the reaction tank while a balance between supply and discharge ismaintained.

In the related art, as a process of performing continuous reaction undera high temperature and a high pressure, for example, a high pressureacid leaching (HPAL) process as described in Patent Document 2 is knownin which nickel oxide ore is charged together with sulfuric acid in anautoclave, a valuable metal such as nickel contained in the ore in atrace amount is leached in a sulfuric acid solution by heating theautoclave to about 250° C., and the valuable metal is recovered.

In the HPAL process, a flash vessel (depressurization tank) and a flashvalve (discharge valve) are provided at an ejection side of theautoclave (reaction tank), control, for example, as disclosed in PatentDocument 3 or Patent Document 4 is performed, and opening and closing ofthe flash valve are repeated while the internal pressure of the reactiontank is managed, so that the continuous operation is executed.

Such a method using the flash vessel and the flash valve is an excellentmethod in which steam generated at the time of depressurization isrecovered as energy and used again. However, it is not easy to apply thecontinuous operation using the reaction tank in a high-pressure state asillustrated in the HPAL process to a complexing reduction process ofobtaining nickel powder by subjecting the aforementioned nickelsulfate-amine complex solution to hydrogen reduction.

The reason for this is that there is a problem in that, since metal ofnickel powder to be produced by reaction is fine and hard, the metal ofnickel powder easily wears out piping or a member attached to the pipingsuch as a valve when the metal of nickel powder is discharged from thereaction tank and cost and time and effort for maintenance are largelyrequired.

In particular, when the pressure is intended to be depressurized fromthe reaction tank to atmospheric pressure, a flow velocity of a nickelpowder-containing slurry passing through the flash valve reaches afurious speed close to a velocity of sound, frictional forcesignificantly increases, and further, the slurry is hit by an inner wallof the flash vessel when the slurry is ejected and recovered, so thatdamage occurs.

Further, in the complexing reduction process, since a liquid in themiddle of the nickel powder being precipitated from the solution isdischarged from the reaction tank in some cases, the liquid isprecipitated also on the inner wall of the piping after discharging tocause clogging, or the liquid is precipitated inside a valve controllingdischarging or the valve traps the nickel powder therein so that openingand closing of the valve cannot be performed.

For this reason, it is necessary to perform maintenance such as frequentdisassembling and washing of piping and a valve, and thus the continuousoperation for a long time is difficult to perform. Further, there is noindustrially actual case of the continuous operation, batch reaction inwhich a liquid is replaced from the reaction tank with respect to eachreaction is a mainstream in commercial production, and a problem of animprovement in productivity arises.

-   Patent Document 1: Japanese Unexamined Patent Application,    Publication No. 2015-212411-   Patent Document 2: Japanese Unexamined Patent Application,    Publication No. 2005-350766-   Patent Document 3: Japanese Unexamined Patent Application,    Publication No. 2010-59489-   Patent Document 4: Japanese Unexamined Patent Application,    Publication No. 2014-240524

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention is proposed in view of such circumstances, and anobject thereof is to provide a method capable of preventing equipment,such as piping and valves, used to discharge and recover a nickelpowder-containing slurry from a high-pressure reaction tank from beingdamaged and trapping the nickel powder therein and enabling thecontinuous operation to improve productivity.

Means for Solving the Problems

The present inventor has conducted intensive studies, and as a result,found that the aforementioned problems can be solved by discharging andtransferring a slurry containing nickel powder obtained in a reactiontank through discharge piping and then supplying a washing solution at apredetermined pressure to the discharge piping to perform a washingtreatment, thereby completing the present invention.

(1) A first invention of the present invention is a nickel powderproduction method, the method including reacting a nickel sulfate-aminecomplex solution with hydrogen gas under a high pressure in a reactiontank to obtain a nickel powder slurry containing nickel powder, in whichthe nickel powder slurry is discharged and transferred through dischargepiping from the reaction tank in which the slurry containing nickelpowder is produced, and then a washing solution is supplied to thedischarge piping at a predetermined pressure to wash the dischargepiping.

(2) A second invention of the present invention is the nickel powderproduction method in the first invention, in which the washing solutionis supplied to the discharge piping at a pressure lower than an internalpressure of the reaction tank by 0.2 MPa to 1.0 MPa.

(3) A third invention of the present invention is the nickel powderproduction method in the first or second invention, in which a filtrateobtained by subjecting the recovered nickel powder slurry tosolid-liquid separation is used as the washing solution.

(4) A fourth invention of the present invention is a nickel powderproduction device in which a nickel sulfate-amine complex solution isreacted with hydrogen gas under a high pressure to obtain a nickelpowder slurry containing nickel powder, the device including: a reactiontank in which a nickel sulfate-amine complex solution is reacted withhydrogen gas to produce nickel powder; a depressurization tank thatdepressurizes the nickel powder slurry discharged from the reaction tankto normal pressure; discharge piping for connecting the reaction tankand the depressurization tank and discharging the nickel powder slurryfrom the reaction tank to the depressurization tank; and washing pipingthat is connected to the discharge piping and supplies a washingsolution to the discharge piping.

Effects of the Invention

According to the present invention, it is possible to prevent equipment,such as piping and valves, used to discharge and recover a nickelpowder-containing slurry from a high-pressure reaction tank from beingdamaged and trapping the nickel powder therein. Accordingly, time andeffort and cost for maintenance are reduced and continuous operation isenabled, so that productivity can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the flow of a nickel powder productionmethod and is a diagram illustrating the flow of a solution or the liketo various treatment tanks.

FIG. 2 is a diagram illustrating a configuration of a nickel powderproduction device.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a specific embodiment of the present invention(hereinafter, referred to as “the present embodiment”) will be describedin detail. Incidentally, the present invention is not limited to thefollowing embodiment, and various modifications can be made within therange that does not change the spirit of the present invention. Further,in the present specification, the description “X to Y” (X and Y arearbitrary numerical values) means “X or more and Y or less” unlessotherwise specified.

<<1. Nickel Powder Production Method>>

A nickel powder production method according to the present embodiment isa method of charging a nickel sulfate-amine complex solution in areaction tank, and reducing nickel ions to nickel in the solution by thesolution being brought into contact with hydrogen gas under pressure,thereby obtaining a nickel powder slurry containing nickel powder.

Specifically, in the production method, the nickel sulfate-amine complexsolution is supplied to the reaction tank and the pressure of a gasphase part inside the reaction tank is adjusted by continuous supply ofhydrogen gas while a temperature inside the reaction tank is maintainedin a predetermined range, so that nickel ions in the nickelsulfate-amine complex solution is reduced to nickel under pressure. Inthe reaction tank, the nickel powder as seed crystals can be addedtogether with the nickel sulfate-amine complex solution, and hydrogenreduction reaction is caused by supplying a mixed slurry of the nickelsulfate-amine complex solution and the nickel powder to the reactiontank, so that nickel produced by reduction is precipitated on thesurface of the nickel powder as seed crystals.

According to such a method, it is possible to efficiently produce nickelpowder having a high quality and an optimum shape by continuousoperation.

(Regarding Hydrogen Reduction Reaction in Reaction Tank)

Specifically, FIG. 1 is a diagram illustrating the flow of a nickelpowder production method and illustrates the flow of a solution or thelike to various treatment tanks. As illustrated in FIG. 1, in theproduction method, first, a mixed slurry of a nickel sulfate-aminecomplex solution and nickel powder (nickel powder slurry) as seedcrystals is supplied to a reaction tank. Then, hydrogen gas forreduction is continuously supplied to the reaction tank in which themixed slurry of a nickel sulfate-amine complex solution and nickelpowder as seed crystals is charged.

The nickel sulfate-amine complex solution is a solution containingnickel in the form of an amine complex, and can be obtained, forexample, by adding ammonia gas or ammonia water (NH₄OH) to a nickelsulfate (NiSO₄) solution.

When the nickel sulfate-amine complex solution is produced, theconcentration of ammonia to be added is not particularly limited, butfor example, it is preferable to add ammonia to be 1.9 or more in amolar ratio with respect to the nickel concentration in the solution.According to this, it can be prevented that nickel in the solutionbecomes nickel hydroxide deposition without forming an amine complex.

As the nickel powder to be added as seed crystals, nickel powder with anaverage particle size of 0.1 μm to 300 μm is preferably used, and nickelpowder with an average particle size of 10 μm to 200 μm is morepreferably used. When the particle size of the nickel powder as seedcrystals is less than 0.1 μm, the nickel powder to be obtained is toofine, and thus there is a possibility that the effect as seed crystalsis not sufficiently exhibited. On the other hand, when the particle sizeof the nickel powder as seed crystals is more than 300 μm, the nickelpowder is coarse, and thus the effect of suppressing abrasion of thefacility is not obtainable and it is economically disadvantageous thatsuch coarse nickel powder is prepared.

As the nickel powder as seed crystals, commercially available nickelpowder can be used, and nickel powder chemically precipitated by a knownmethod can be classified and used. Further, produced nickel powder canalso be repeatedly used. Incidentally, the nickel powder as seedcrystals is continuously supplied together with the nickel sulfate-aminecomplex solution as a raw material to the reaction tank by a supplydevice such as a slurry pump.

The temperature inside the reaction tank, that is, the reactiontemperature of the hydrogen reduction reaction is set to a range of 150°C. to 250° C. Further, the temperature is set preferably to 150° C. to185° C. The temperature inside the reaction tank is adjusted, forexample, by heating using a heating device or the like, and ismaintained. When the reaction temperature is lower than 150° C.,reduction efficiency of nickel ions in the nickel sulfate-amine complexsolution is degraded. On the other hand, even when the reactiontemperature is higher than 250° C., the reduction reaction is notaffected, and instead, the loss of hydrogen gas to be supplied to thereaction tank and the loss of thermal energy occur.

In this production method, in a state where the temperature of thereaction tank is maintained at 150° C. to 250° C., hydrogen gas iscontinuously supplied to the gas phase part at which the solution is notfilled in the reaction tank. By supplying the hydrogen gas in this way,the pressure of the gas phase part is set, for example, to a range of2.5 MPa to 3.5 MPa. Specifically, hydrogen gas is directly blown to thegas phase part in the reaction tank, for example, from a cylinder or thelike, or is blown into the slurry.

Regarding the pressure of the gas phase part, when the internal pressureis less than 2.5 MPa, the efficiency of reduction reaction of nickelions is degraded. On the other hand, even by setting a high pressurecondition such that the internal pressure is more than 3.5 MPa, thereduction reaction is not affected, and instead, the loss of thesupplied hydrogen gas increases.

As described above, in the nickel powder production method according tothe present embodiment, hydrogen gas is blown to the mixed slurry of anickel sulfate-amine complex solution and nickel powder as seed crystalsto adjust the pressure to a predetermined pressure, so that nickel ionscontained in the nickel sulfate-amine complex solution is reduced tonickel under pressure. According to this, nickel produced by reductionis precipitated on the surface of the nickel powder supplied as seedcrystals so that reduced nickel powder can be obtained.

(Regarding Extraction of Nickel Powder Slurry)

Next, the nickel powder slurry containing nickel powder that is areacted slurry produced in the reaction tank is discharged and extractedfrom the reaction tank to a depressurization tank. The nickel powderslurry is produced by reduction reaction in the reaction tank underpressure and has an extremely high pressure. Therefore, by dischargingand transferring such a nickel powder slurry to the depressurizationtank, the pressure is gradually reduced in the depressurization tank,and for example, is set to the same pressure as atmospheric pressure.

The reaction tank and the depressurization tank are connected by piping(discharge piping) for transferring the nickel powder slurry, and thenickel powder slurry ejected from the reaction tank is discharged to thedepressurization tank through the discharge piping.

Herein, in the nickel powder production method according to the presentembodiment, the nickel powder slurry produced in the reaction tank isdischarged and transferred through the discharge piping, and then awashing solution is supplied at a predetermined pressure to thedischarge piping to wash the inside of the discharge piping or a valveprovided in the discharge piping. According to such a method, it ispossible to wash and remove nickel powder and other precipitatesprecipitated during the process of discharging the nickel powder slurry,nickel powder trapped in the valve, and the like, and it is possible toeffectively prevent abrasion and clogging of the piping and the valvescaused by the precipitated nickel powder, or the like. According tothis, time and effort and cost for maintenance can be effectivelyreduced and the continuous operation is enabled, so that productivitycan be improved.

Incidentally, washing of the discharge piping using the washing solutionwill be described in detail together with the description of theconfiguration of a production device described later.

(Regarding Recovery of Nickel Powder from Nickel Powder Slurry)

When the pressure of the nickel powder slurry is reduced in thedepressurization tank to atmospheric pressure, next, the nickel powderslurry is extracted from the depressurization tank and transferred to asolid-liquid separation tank.

In the solid-liquid separation tank, the nickel powder slurry issubjected to a solid-liquid separation treatment based on a knownmethod, so that the nickel powder slurry is separated into nickel powderand a filtrate to recover nickel powder. Incidentally, althoughspecifically described later, the filtrate separated herein can bereused as the washing solution of the discharge piping in order totransfer the nickel powder slurry from reaction tank to thedepressurization tank.

<<2. Nickel Powder Production Device>>

Next, a production device for performing the nickel powder productionmethod will be described in more detail. The nickel powder productionmethod according to the present embodiment can be performed using anickel powder production device to be described specifically below.

FIG. 2 is a diagram illustrating an example of the configuration of anickel powder production device. This nickel powder production device 1is a production device in which a nickel sulfate-amine complex solutionis reacted with hydrogen gas under a high pressure to obtain a nickelpowder slurry containing nickel powder.

Specifically, a nickel powder production device 1 (hereinafter, simplyalso referred to as “production device 1”) includes a reaction tank 11in which a nickel sulfate-amine complex solution is reacted withhydrogen gas, a depressurization tank 12 that depressurizes the nickelpowder slurry produced in the reaction tank 11 to normal pressure, anddischarge piping 13 that connects the reaction tank 11 and thedepressurization tank 12 and discharges and transfers the nickel powderslurry. Further, this production device 1 is provided with washingpiping 14 that is connected to the discharge piping 13 and supplies awashing solution to the discharge piping 13.

As described above, in the nickel powder production device 1, byproviding the washing piping 14 connected to the discharge piping 13,the washing solution is supplied to the discharge piping 13 so that itis possible to effectively wash the inside of the discharge piping 13 ora valve and the like provided in the discharge piping 13, and thusoperation failure is prevented to enable stable operation andimprovement in production efficiency can be achieved.

[Reaction Tank]

The reaction tank 11 is a place in which the nickel sulfate-aminecomplex solution is reacted with hydrogen gas. In this reaction tank 11,the reaction in which nickel ions in the nickel sulfate-amine complexsolution are reduced to produce nickel powder, is caused by the suppliedhydrogen gas. For example, hydrogen reduction reaction is caused byadjusting and maintaining the pressure of the gas phase part inside thereaction tank 11 to a range of 2.5 MPa to 3.5 MPa by continuous supplyof hydrogen gas.

The reaction tank 11 is not particularly limited as long as it is apressurized reaction tank which can be adjusted to a predeterminedtemperature condition and a predetermined pressure condition andmaintained. For example, an autoclave or the like can be used. Thematerial of the autoclave is not particularly limited, and for example,an autoclave made of austenitic stainless steel such as SUS316L orSUS304L can be used. Further, the size thereof can also be appropriatelyset depending on a treated amount of the mixed slurry of a nickelsulfate-amine complex solution as a raw material and nickel powder asseed crystals, or the like.

The reaction tank 11 is provided with at least a charging port 11A inwhich the nickel sulfate-amine complex solution as a raw material ischarged, a hydrogen gas supply port 11B to which hydrogen gas forhydrogen reduction is supplied, and an ejection port 11C that ejects(discharges) a slurry containing nickel powder produced by hydrogenreduction reaction (nickel powder slurry).

(Charging Port)

The charging port 11A is connected to charging piping (not illustrated),and is connected, for example, to a storage tank for the nickelsulfate-amine complex solution by the charging piping. In the reactiontank 11, the nickel sulfate-amine complex solution transferred throughthe charging piping is charged in the inside through the charging port11A. Incidentally, the raw material charged from the charging port 11Amay be the nickel sulfate-amine complex solution alone or may be a mixedslurry obtained by mixing nickel powder as seed crystals in the complexsolution in advance.

(Hydrogen Gas Supply Port)

The hydrogen gas supply port 11B is connected to hydrogen gas supplypiping 21, and is connected, for example, to a hydrogen gas supplydevice such as a hydrogen gas cylinder by the hydrogen gas supply piping21. In the reaction tank 11, hydrogen gas supplied through the hydrogengas supply piping 21 is supplied to the inside through the hydrogen gassupply port 11B.

Herein, the hydrogen gas supply piping 21 is, as described above, pipingthat is connected to a hydrogen gas cylinder or the like and is used forsupplying hydrogen gas into the reaction tank 11. In this hydrogen gassupply piping 21, a gas supply valve 21 a is provided at a predeterminedposition and the supply of hydrogen gas is controlled. Incidentally, thegas supply valve 21 a may be an ON/OFF valve that controls ON (withsupply) and OFF (without supply) of the supply of hydrogen gas, or maybe a control valve that can control the amount of hydrogen gas supplied.

(Ejection Port)

The ejection port 11C is an ejection port for ejecting and dischargingthe nickel powder slurry produced by hydrogen reduction reaction in thereaction tank 11 from the reaction tank 11. The discharge piping 13described later is connected to the ejection port 11C, and the nickelpowder slurry ejected from the ejection port 11C is discharged andtransferred to the depressurization tank 12 through the discharge piping13.

[Depressurization Tank]

The depressurization tank 12 is a tank for depressurizing the nickelpowder slurry produced in the reaction tank 11, for example, to normalpressure. The depressurization tank 12 includes, for example, a flashtank (flash vessel).

The depressurization tank 12 is provided with a charging port 12A forcharging the nickel powder slurry discharged from the reaction tank 11in the inside at a predetermined position of the top board thereof. Thecharging port 12A is connected to the discharge piping 13 describedlater, and the nickel powder slurry from the reaction tank 11 istransferred through the discharge piping 13 and charged in the inside ofthe depressurization tank 12 through the charging port 12A.

[Discharge Piping]

The discharge piping 13 is piping for connecting the reaction tank 11and the depressurization tank 12 and discharging and transferring thenickel powder slurry produced in the reaction tank 11 to thedepressurization tank 12. The nickel powder slurry discharged from thereaction tank 11 and passing through the discharge piping 13 is in astate of maintaining a high pressure, and the nickel powder slurry flowsin the discharge piping 13 at a flow velocity close to a velocity ofsound under the high pressure and is charged in the depressurizationtank 12.

The discharge piping 13 is provided with at least an ejection valve 13 apositioned in the vicinity of the reaction tank 11 side and a flashvalve 13 b positioned in the vicinity of the depressurization tank 12.

(Ejection Valve)

The ejection valve 13 a is a control valve for controlling the amount ofthe nickel powder slurry ejected from the ejection port 11C of thereaction tank 11, that is, the amount of the nickel powder slurrytransferred in the discharge piping 13. The ejection valve 13 a may bean ON/OFF valve that controls ON (with transfer) and OFF (withouttransfer) of the transfer of the nickel powder slurry, or may be acontrol valve that can control the amount of the nickel powder slurrytransferred.

(Flash Valve)

The flash valve 13 b is a control valve for controlling charging thenickel powder slurry when the nickel powder slurry transferred throughthe inside of the discharge piping 13 is charged in the depressurizationtank 12. When the nickel powder slurry is charged in thedepressurization tank 12 by opening and closing the flash valve 13 bwhile the internal pressure of the reaction tank 11 is appropriatelymanaged, the continuous operation can be performed. The flash valve 13 bmay be an ON/OFF valve that controls ON (with charge) and OFF (withoutcharge) of the charging of the nickel powder slurry to thedepressurization tank 12, or may be a control valve that can control theamount of the nickel powder slurry charged.

[Washing Piping]

The washing piping 14 is piping that is connected to the dischargepiping 13 and supplies a washing solution to the discharge piping 13.The washing piping 14 is connected, for example, to the discharge piping13 while branching is provided at a predetermined site of the dischargepiping 13 (for example, “P” in FIG. 2). A connection site on thedischarge piping 13 with the washing piping 14 is not particularlylimited, but can be a site in the vicinity of the ejection valve 13 a orin the vicinity of the flash valve 13 b, and can be an intermediateposition of the discharge piping 13 connecting the reaction tank 11 andthe depressurization tank 12.

The washing piping 14 is provided with a washing solution supply valve14 a. The washing solution supply valve 14 a is provided in the vicinityof a washing solution tank storing a washing solution to be supplied tothe discharge piping 13 through the washing piping 14, or the like andcontrols the supply of the washing solution. The washing solution supplyvalve 14 a may be an ON/OFF valve that controls ON (with supply) and OFF(without supply) of the supply of the washing solution through thewashing piping 14, or may be a control valve that can control the amountof the washing solution transferred.

The nickel powder production device 1 according to the presentembodiment includes, as described above, the washing piping 14 connectedto the discharge piping 13 for discharging the nickel powder slurry fromthe reaction tank 11, and by supplying the washing solution to thedischarge piping 13 through the washing piping 14, the inside of thedischarge piping 13 or a valve (the ejection valve 13 a or the flashvalve 13 b) and the like provided in the discharge piping 1 can bewashed. According to this, the nickel powder and other precipitatesprecipitated to the discharge piping 13, the flash valve 13 b, and thelike can be washed and removed, and for example, clogging or trapping ofthe flash valve 13 b can be effectively prevented.

The washing solution is not particularly limited, and for example, water(washing water) or the like can be used. Further, other than this, draingenerated after heat is recovered from steam generated when pressure isdepressurized to normal pressure in the depressurization tank can beused, and further, a filtrate obtained by subjecting the recoverednickel powder slurry to solid-liquid separation by a known method may bereused.

Further, inert gas supply piping 22 for supplying an inert gas such asnitrogen gas or argon gas is connected to the washing piping 14 at apredetermined position. The inert gas such as nitrogen gas is used foradjusting the internal pressure of the washing piping 14 and thedischarge piping 13 to adjust the pressure when the washing solution issupplied from the washing piping 14 to the discharge piping 13. Theinert gas supply piping 22 is connected, for example, to a gas cylinderfor nitrogen gas or the like and is provided with a gas supply valve 22a for adjusting the flow rate of gas at a predetermined position. Thepressure of the inert gas is controlled by the gas supply valve 22 a andthe inert gas is supplied to the washing piping 14 through the inert gassupply piping 22.

Incidentally, the pressure of the washing solution is not limited to becontrolled by the supply of the inert gas as described above, but forexample, a liquid feeding pump may be connected to the washing piping 14and the washing solution in the washing piping 14 may be pressurized.Further, by the aforementioned inert gas supply piping 22 beingconnected directly to a washing solution storage tank connected with thewashing piping 14, the inert gas may be supplied into the storage tank,so that the washing solution can be supplied at a predeterminedpressure.

(Supply of Washing Solution Through Washing Piping)

Herein, it is preferable to supply, to the washing piping 14, thewashing solution at a pressure lower than the internal pressure of thereaction tank 11 by a range of 0.2 MPa to 1.0 MPa. Further, morepreferably, the pressure is set to be lower than the internal pressureof the reaction tank 11 by a range of 0.5 MPa to 1.0 MPa. Incidentally,the pressure of the washing solution is, as described above, controlledby the gas supply valve 22 a provided in the washing piping 14.Specifically, since the internal pressure in the reaction tank 11 ismaintained in a range of 2.5 MPa to 3.5 MPa by the supply of hydrogengas, the washing solution is supplied through the washing piping 14 at apressure lower than the internal pressure of the reaction tank 11 by arange of 0.2 MPa to 1.0 MPa, for example, at a pressure of 2.0 MPa to2.5 MPa.

When a difference between the supply pressure of the washing solutionand the internal pressure of the reaction tank 11 is less than 0.2 MPa,the removal force by the flow velocity at the time of supplying thewashing solution becomes small and thus there is possibility thatsufficient washing cannot be performed. On the other hand, even when thedifference with the internal pressure of the reaction tank 11 is largerthan 1.0 MPa, the washing effect is not further improved, and instead,there is possibility that piping and valves are worn out or damaged bythe nickel powder removed by washing, or the like.

Examples

Hereinafter, the present invention will be described in more detail bymeans of Examples of the present invention, but the present invention isnot limited to the following Examples at all.

Example 1

Nickel powder was produced using the device as schematically illustratedin FIG. 2. That is, an autoclave made of austenitic stainless steel suchas SUS316L or SUS304L with a capacity of 200 L was used as a reactiontank, and hydrogen gas was continuously supplied to a nickelsulfate-amine complex solution to cause hydrogen reduction reaction.Further, a flash tank with a capacity of 1000 L was used as adepressurization tank, and a slurry of the nickel powder produced in thereaction tank was charged in the flash tank and was depressurized toatmospheric pressure. Then, the reaction tank and the depressurizationtank were connected by discharge piping with an inner diameter of 10 mm.Incidentally, an ejection valve was provided at an ejection port of thereaction tank, a flash valve for controlling the charging of the nickelpowder slurry into the depressurization tank was provided at a ceilingpart of the depressurization tank, and charging control was performed byopening and closing the valve.

Further, in the production device, washing piping was connected whilebranching was provided in the middle of the discharge piping, and awashing solution was enabled to be supplied to the discharge pipingthrough the washing piping. Incidentally, the washing piping wasconnected while branching was provided at the side close to the reactiontank in the discharge piping. Further, piping for industrial water wasconnected to the washing piping, and the industrial water as the washingsolution was supplied under the supply control by a washing solutionsupply valve. Furthermore, supply piping supplying nitrogen gas as aninert gas was connected to the washing piping, and the nitrogen gas wasenabled to be supplied under the supply control by a gas supply valve.

The nickel sulfate-amine complex solution with a nickel concentration of82.5 g/L was supplied at a flow rate of 1.0 L/min to the reaction tankby using such a production device. Further, a slurry containing 33 g/Lof nickel powder with a diameter of 75 μm or less as seed crystals wassupplied at a flow rate of 0.5 L/min.

Further, the internal temperature of the reaction tank was maintained at185° C., and the pressure inside the reaction tank was adjusted to arange of 2.5 MPa to 3.5 MPa by blowing hydrogen gas from a cylinder.Incidentally, in order to maintain the amount of the solution in thereaction tank to be 90 L, the flash valve attached to the top part ofthe depressurization tank was intermittently opened and closed toextract the nickel powder slurry into the depressurization tank throughthe discharge piping.

After the nickel powder was extracted, the ejection valve of thereaction tank and the flash valve were sequentially closed in thisorder. Next, the washing solution supply valve Provided in the washingpiping was opened to supply 4 L of washing solution (industrial water)into the discharge piping through the washing piping, and then thewashing solution supply valve was closed. Incidentally, 1 to 2 L spacewas allowed to remain inside the washing piping and the dischargepiping. Then, the gas supply valve was opened to adjust the internalpressure of the washing piping and the discharge piping to a range of2.0 MPa to 2.5 MPa that is lower than the internal pressure of thereaction tank by 0.5 MPa to 1.0 MPa, and the washing solution wassupplied to the discharge piping at such a pressure.

The discharge piping and the flash valve were washed by opening theflash valve under the supply of the washing solution through the washingpiping. After the completion of washing, the ejection valve of thereaction tank and the flash valve were opened, and discharging of thenickel powder slurry from the reaction tank to the depressurization tankwas repeated.

Although the operation as described above was continued for 6 hours,abrasion, or adhering or trapping of the nickel powder or the like inthe flash valve and the discharge piping did not occur, and it waspossible to stably perform extraction of the nickel powder slurry fromthe reaction tank to the depressurization tank without any trouble.

Example 2

The operation was performed using the same production device as inExample 1, except that the washing piping was connected to a 350 Lwashing solution storage tank, and nitrogen gas supply piping wasconnected directly to the washing solution storage tank to enablenitrogen gas to be supplied.

As the washing solution, 300 L of filtrate obtained by subjecting thenickel powder slurry recovered from the depressurization tank by theoperation in Example 1 to solid-liquid separation using Nutsche wasused. Incidentally, the filtrate was stored in the washing solutionstorage tank and used as the washing solution. Further, nitrogen gas wassupplied to the washing solution storage tank to adjust the internalpressure of the washing solution storage tank to a range of 2.0 MPa to2.5 MPa, the washing solution supply valve was controlled such that 4 Lof the washing solution was ejected at one time, and the washingsolution was supplied to the discharge piping through the washingpiping.

Although the operation as described above was continued for 7 hours,abrasion, or adhering or trapping of the nickel powder or the like inthe flash valve and the discharge piping did not occur, and it waspossible to stably perform extraction of the nickel powder slurry fromthe reaction tank to the depressurization tank without any trouble.

Comparative Example 1

The operation was performed using the same production device as inExample 1, except that the washing piping was not provided. That is, theoperation was performed using the production device not including themechanism of supplying the washing solution to the discharge piping at apredetermined pressure.

Although the operation was performed for 6 hours under the samecondition as in Example 1, after 1 hour from the operation start,opening and closing of the flash valve were not able to be controlled,an excessive amount of the nickel powder slurry was discharged andtransferred from the reaction tank to the depressurization tank, so thatthe amount of the solution in the reaction tank was not able to bemaintained to 90 L and the operation was stopped.

After the operation stop, when the flash valve was observed, the nickelprecipitate or fine nickel powder was precipitated or trapped in thevalve.

EXPLANATION OF REFERENCE NUMERALS

-   1 NICKEL POWDER PRODUCTION DEVICE-   11 REACTION TANK-   11A CHARGING PORT-   11B HYDROGEN GAS SUPPLY PORT-   11C EJECTION PORT-   12 DEPRESSURIZATION TANK-   12A CHARGING PORT-   13 DISCHARGE PIPING-   13 a EJECTION VALVE-   13 b FLASH VALVE-   14 WASHING PIPING-   14 a WASHING SOLUTION SUPPLY VALVE-   21 HYDROGEN GAS SUPPLY PIPING-   21 a GAS SUPPLY VALVE-   22 INERT GAS SUPPLY PIPING-   22 a GAS SUPPLY VALVE

1. A nickel powder production method, the method comprising reacting anickel sulfate-amine complex solution with hydrogen gas under a highpressure in a reaction tank to obtain a nickel powder slurry containingnickel powder, wherein the nickel powder slurry is discharged andtransferred through discharge piping from the reaction tank in which theslurry containing nickel powder is produced, and then a washing solutionis supplied to the discharge piping at a predetermined pressure to washthe discharge piping.
 2. The nickel powder production method accordingto claim 1, wherein the washing solution is supplied to the dischargepiping at a pressure lower than an internal pressure of the reactiontank by 0.2 MPa to 1.0 MPa.
 3. The nickel powder production methodaccording to claim 1, wherein a filtrate obtained by subjecting therecovered nickel powder slurry to solid-liquid separation is used as thewashing solution.
 4. A nickel powder production device in which a nickelsulfate-amine complex solution is reacted with hydrogen gas under a highpressure to obtain a nickel powder slurry containing nickel powder, thedevice comprising: a reaction tank in which a nickel sulfate-aminecomplex solution is reacted with hydrogen gas to produce nickel powder;a depressurization tank that depressurizes the nickel powder slurrydischarged from the reaction tank to normal pressure; discharge pipingfor connecting the reaction tank and the depressurization tank anddischarging the nickel powder slurry from the reaction tank to thedepressurization tank; and washing piping that is connected to thedischarge piping and supplies a washing solution to the dischargepiping.
 5. The nickel powder production method according to claim 2,wherein a filtrate obtained by subjecting the recovered nickel powderslurry to solid-liquid separation is used as the washing solution.